Scientific Ninja writes: "Astronomers in the University of Sydney have captured pictures of a 'union' between our closest neighbouring galaxy, Andromeda, and its smaller neighbour, the Triangulum Galaxy.
Published in the journal Nature on 3 September 2009, the research shows how large galaxies grow by incorporating stars from surrounding smaller galaxies. This popular model of galaxy evolution, called the 'hierarchical model', predicts that large galaxies such as Andromeda, which can be seen with the naked eye from the northern hemisphere, should be surrounded by relics of smaller galaxies it has connected with."Link to Original Source